Field of Invention
More particularly, the present invention is related to a nano-electromechanical switch and to a method for designing such a nano-electromechanical switch.
Description of the Related Art
As power and energy constraints in microelectronic applications become more challenging an alternative and more power efficient ways of switching and computing is desired. A conventional switching device used in the semiconductor industry is a C-MOS transistor. To overcome power related power bottlenecks in C-MOS devices switching devices, which operate on fundamentally different transport mechanisms such as tunneling, are investigated. However, combining the desirable characteristics of high on-current, very low off-current, abrupt switching, high speed as well as a small footprint in a device that might be easily interfaced to a C-MOS device is a challenging task. Mechanical switches such as nano-electromechanical switches (NEM switches) are promising devices to meet these kinds of criteria. A nano-electromechanical switch has a narrow gap between electrodes and is controlled by electrostatic actuation. In response to an electrostatic force, a contact electrode can be bent to contact another electrode and therefore close the switch. A main issue in designing and operating nano-electrochemical switches is to control the narrow gap for the electrostatic actuation and for the electrical contact separation. A nano-electromechanical switch has to meet both requirements of high switching speed and low actuation voltage.
Common electromechanical switches use straight cantilever beams as switching elements, which is not the best solution to meet these requirements.
FIG. 1A and FIG. 1B illustrate the structure of a conventional nano-electromechanical switch having a straight cantilever beam CB. FIG. 1A shows a straight cantilever beam CB being in an initial position IP and being attracted by an actuation electrode AE when an activation voltage is applied between the actuator electrode and the cantilever beam CB. In a contact position CP the distal end of the cantilever beam CB contacts an output electrode and provides an electrical contact between the cantilever beam CB and the output electrode of the nano-electromechanical switch. Referring to FIG. 1A, the flexing of the cantilever beam CB is distributed over the whole beam length. As a result, the remaining gap between the cantilever beam CB and the actuator electrode AE is uneven and not uniform. The remaining gap becomes very small leading to high electrical field E close to the distal end, which leads to a low robustness due to electrical or mechanical breakdown. Referring to FIG. 1B, the robustness of the nano-electromechanical switch has a straight cantilever beam CB, which can be improved by increasing the width of the cantilever beam CB. However, the straight cantilever beam CB still results in a strong electrical field E when the actuator electrode AE is placed close to the contact point between the cantilever beam CB and the output electrode OE as described in R. Parsa, M. Shawezipur, W. S. Lee, S. Chong, D. Lee, H. S. P. Wong, R. Marboudian, R. T. Howe “Nano-electromechanical relays with decoupled electrode and suspension” IEEE MEMS conference, 2011.
To increase the robustness of the nano-electromechanical switch, a parallel motion switch has been proposed. As depicted in FIG. 2, to obtain high robustness the force Fel between the actuation electrode AE and the cantilever beam CB in the closed state is minimized in order to avoid a pull-in of the cantilever beam CB onto the actuation electrode AE. This is done by minimizing the electrical field E, which is equivalent to the force Fel by adapting the angle β (β=90−α) between the direction of motion DOM and the actuator electrode AE.
                              gap          R                =                              (                                                            gap                  0                                                  cos                  ⁡                                      (                    α                    )                                                              -                              gap                0                                      )                    ·                      cos            ⁡                          (              α              )                                                          (        1        )                                          V          pi                =                                            8              27                        ⁢                                                                                k                    m                                    ⁢                                      gap                    0                    3                                                                                        ɛ                    0                                    ⁢                                      A                    el                                                              ·                              cos                ⁡                                  (                  α                  )                                                                                        (        2        )                                          E                      ma            ⁢                                                  ⁢            x                          ≥                              V            pi                                gap            R                                              (        3        )                            where gap0 is the initial gap between the distal end of the cantilever beam CB and the output electrode OE,        gapR is the remaining gap in the closed state of the nano-electromechanical switch,        km is a mechanical spring constant,        ∈0 is the dielectric permittivity of air and        Emax is the electric field strength in a closed state of the nano-electromechanical switch,        Vpi is the pull-in voltage,        Ael is the area of the electrode, and        α is an inclination angle of the cantilever beam CB.        
Referring to FIG. 2, the actuation electrode AE has an inclination angle α with respect to the direction of motion DOM to avoid a complete closure and a shortcut of the actuation electrode with the inclined cantilever beam. The disadvantage of a conventional parallel motion switch is that to ensure a parallel motion such a nano-electromechanical switch as shown in FIG. 2, is large and not suited for VLSI NEM switch technology.